1. Field of the Invention
This invention relates in general to traction and hydraulic elevator system with distributed control circuits, and more particularly, to a method and control system for protecting against control signal and communication failures, with diminished or excessively restrictive elevator service, because of the loss of a vital element in the system.
2. Description of the Prior Art
Computers have heretofore been pre-programmed to perform various functions in the operational control or management of car and hall call response strategies in an elevator system such as in U.S. Pat. No. 4,511,017 which provides emergency back-up elevator service, when normal service is degraded, by preassigning and revising blocks of car assignments to floors in a rotational manner.
Various arrangements for elevator bank configurations have been known to benefit from these state-of-the-art solid-state controllers, but assuming that dynamically defined tasks involve uniquely reconfigured failure mode arrangements; these have yet to emerge to a level that is highly efficient and least restrictive. Disturbingly present is the likelihood that the failure of components, assigned for dedicated control functions such as in a fixed dispatcher controller, used with the present day elevator control apparatus, will eventually interrupt or discontinue to communicate with other controllers in the system. These systems may have a back-up mode of operation with some form of service being retained, but it may be of significantly inferior quality to the normal service.
With the introduction of microprocessor based elevator controllers and the distribution of electronic circuits located with each car and proximate to the respective floors, communication with the remote controllers is of fundamental concern since the integrity of hall call signals, and the control strategy in assigning cars to answer these calls, is critical to operational efficiency and to the satisfied customer. Prospective passengers, if possible, should not be aware of or a witness to degradation of service.
One of the principal problems with a distributed control system for controlling a plurality of elevator cars is that normally the remote controller which has been selected for implementing the control strategy is also responsible for checking the integrity of the communication with the other controllers in the system. In some failure modes the other controllers may not be immediately informed and they don't assume the self-selection necessary to begin implementing a master control or other effective strategy remaining available to them such as if there remains good signal integrity between this controller and the hallway serial link of corridor communication.
Another problem is in the situation where there is a failure of the master controller because of one of the hallway serial links becoming interrupted and the remaining controllers become disjointed for the bank of cars because there is no priority of command for controllers. There may be insufficient communication to alert each controller as to the least restrictive operation for each of the controllers in the system. Asserting the authority as master controller by each would result in the potential for multiple car assignments to the same floor unless the remaining controllers continue to communicate with each other without further interruption. Otherwise, all cars going on block operation inexcusably may not be the best car efficiency for the bank of cars which still has the potential for providing more efficient service and to minimize waiting time.